This invention relates generally to the field of cataract surgery and more particularly to a method of operating a surgical system or console.
The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of the lens onto the retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and lens.
When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL).
In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, a thin phacoemulsification cutting tip is inserted into the diseased lens and vibrated ultrasonically. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an artificial lens.
A typical ultrasonic surgical device suitable for ophthalmic procedures consists of an ultrasonically driven handpiece, an attached cutting tip, and irrigating sleeve and an electronic control console. The handpiece assembly is attached to the control console by an electric cable and flexible tubings. Through the electric cable, the console varies the power level transmitted by the handpiece to the attached cutting tip and the flexible tubings supply irrigation fluid to and draw aspiration fluid from the eye through the handpiece assembly.
The operative part of the handpiece is a centrally located, hollow resonating bar or horn directly attached to a set of piezoelectric crystals. The crystals supply the required ultrasonic vibration needed to drive both the horn and the attached cutting tip during phacoemulsification and are controlled by the console. The crystal/horn assembly is suspended within the hollow body or shell of the handpiece by flexible mountings. The handpiece body terminates in a reduced diameter portion or nosecone at the body's distal end. The nosecone is externally threaded to accept the irrigation sleeve. Likewise, the horn bore is internally threaded at its distal end to receive the external threads of the cutting tip. The irrigation sleeve also has an internally threaded bore that is screwed onto the external threads of the nosecone. The cutting tip is adjusted so that the tip projects only a predetermined amount past the open end of the irrigating sleeve.
In use, the ends of the cutting tip and irrigating sleeve are inserted into a small incision of predetermined width in the cornea, sclera, or other location. The cutting tip is ultrasonically vibrated along its longitudinal axis within the irrigating sleeve by the crystal-driven ultrasonic horn, thereby emulsifying the selected tissue in situ. The hollow bore of the cutting tip communicates with the bore in the horn that in turn communicates with the aspiration line from the handpiece to the console. A reduced pressure or vacuum source in the console draws or aspirates the emulsified tissue from the eye through the open end of the cutting tip, the cutting tip and horn bores and the aspiration line and into a collection device. The aspiration of emulsified tissue is aided by a saline flushing solution or irrigant that is injected into the surgical site through the small annular gap between the inside surface of the irrigating sleeve and the cutting tip. Once the hard parts of the lens is emulsified and removed, the ultrasonic cutting step is typically followed by Irrigation/Aspiration (I/A) step that removes the softer lens material by aspirating only.
While the fragments of the material to be aspirated are reduced to the size which may flow uninhibited through tip of the handpiece, occasionally they block the aspiration port without going though. In these cases the user typically vents (i.e. releases vacuum from the aspiration line). The act of venting allows user to release the blocking fragment, so he/she can reposition it, to attempt further aspiration. Also in some instances, the aspiration port may accidentally capture a tissue that was not intended for aspiration, such as iris or posterior capsule. In these cases the user employs venting as well, to release the captured tissue to prevent tissue damage.
Venting process typically involves opening a vent valve to release vacuum and bringing system pressure to vent source pressure. Depending on the venting system type (fluid or air vented) the vent source pressure would vary. For example air vented system would vent to the ambient pressure (i.e. 0.) A liquid venting system may vent to the irrigation bottle, i.e. to the hydrostatic pressure that is function of the bottle height. Also, some instruments may utilize different or additional methods of venting, such as aspiration pump reversal. In all cases, the system pressure is automatically brought to a fixed level determined by the system design.
While fixed pressure venting typically accomplishes the task, wide variety of the modern phaco tips and accessories, as well as wide range of a modern system settings (such bottle height and vacuum limit), can affect the consistency of the venting action user gets. In addition, a variety of evolved user techniques contributes to the variability of the vent performance. For example, a certain user technique can result in under-venting, forcing user to use reflux more often. In other cases, a user technique can be prone to over-venting, resulting in excessive lens material regurgitation. Depending upon the surgical technique being employed, this automatic operation can result to too much or too little vacuum being vented. This is particularly true with the large number of different types of tips, techniques and accessories currently available.
Therefore, a need continues to exist for a method of variably controlling aspiration venting on surgical consoles.